In production system, manufacturing process sometimes shift into abnormal situation. When the manufacturing process is out of control, managers applied all kinds of quality-improving strategies to improve their product qualities within the required specification and stable. Besides, different quality-improving strategies have very complex relationship between quality costs and revenue. So, under the frame of statistic process control and aiming at the abnormal situation of manufacturing process, we discuss what the cost be paid and how much revenue be earned by taking different quality-improving strategies. Under the consideration of the products is repairable and the viewpoint of quality cost and benefit, we can build a incremental profit model on quality and cost and search for the optimal quality-improving strategy to maximize the incremental profit. Furthermore, we also proposed a numerical example to illustrate the meaning of this research and the result, which could be used by the later researches and actual applications.